1. Field of the Invention
The present invention relates to a head for checking linear dimensions, such as dimensions of workpieces, with a support; an arm--movable with respect to the support--, which defines a longitudinal geometric axis; a feeler arranged at an end of the movable arm; means, for connecting the arm to the support, comprising portions elongated mainly along directions perpendicular to said longitudinal axis, one of the portions being secured to the support and another being secured to the arm, and fulcrum means adapted to permit mutual displacements of the portions, the displacements essentially and only consisting of mutual rotations about at least one axis being transversal with respect to the longitudinal axis; thrust means for defining a rest position of the movable arm; and detecting means responsive to the displacements of the movable arm from the rest position.
2. Description of the Prior Art
As it is known, presently there is an increasing trend to provide turning machines and machining centers with heads for checking the linear dimensions of the workpieces, machined or to be machined, and of the tools. These heads normally comprise an arm carrying a feeler adapted to contact the workpiece and the tool, a support, devices for connecting the arm to the support--which permit displacements of the feeler along one or more axes--and detecting devices. The detecting devices can include position transducers, which provide measurement signals (normally of comparative type), or electrical contacts which open as a consequence of the mechanical contact between the feeler and the workpiece (or the tool). In the second case, the opening of the electrical contacts provides a logic signal which controls reading of measurement signals provided by transducers associated with the machine tool slide/s where there are arranged the head, and/or the workpiece, and/or the tool.
It is evident that sturdiness and repeatability are basic requirements for heads to be employed for the above-stated uses.
Moreover, the dimensions of the heads often must be small, due to problems of space for the particular type of connection and storage within the machine tool, particularly with regard to lathes provided with automatic systems for tool replacement.
Another important requirement for these heads is a rather broad amplitude of the displacements of the movable arm, in order to obtain measurement ranges of high value (as far as measuring heads are concerned) and/or for reasons of safety. Of course, if the overall dimensions of the head are very small, it becomes difficult to obtain long displacements of the movable arm while contemporaneously guaranteeing sturdiness and repeatibility of the head.
The known heads do not provide a satisfactory compromise between these contrasting requirements.
In fact, either the repeatability is impaired by excessive plays and consequent undesired motions among the electrical components, or the amplitude of the displacements is too limited due to the dimensions of the head itself.
Italian patent application No. 3578A/81 filed on Nov. 20, 1981 describes a measuring head in which the device connecting the arm to the support is obtained by means of an integral member having portions with reduced thickness, which define the fulcrums about which the movable arm can perform rotational displacements. However, just in view of the type of their construction, these fulcrums permit angular movements of small amplitude, so that, in order to obtain measurement ranges of broad value, it is necessary to foresee considerable dimensions for the integral member and thus for the head.